1. Field of the Invention
The present invention relates to a semiconductor device constructed by combining a movable element such as a surface acoustic wave filter and other semiconductor elements.
2. Description of Related Art
For example, in a mobile telephone set represented by an automobile telephone set or a portable telephone set, a surface acoustic wave (SAW: Surface Acoustic Waves) filter has been employed for signal processing in a high frequency band. The surface acoustic wave filter converts an electric signal into surface acoustic waves propagating through a surface layer of an elastic member, and takes out the surface acoustic waves which have propagated through the surface of the elastic member as an electric signal. The surface acoustic wave filter is constructed by forming comb-shaped electrodes on the surface of a solid such as silicon. Frequency characteristics can be determined by the shape, for example, of the electrodes, thereby making it possible to construct a filter having desired frequency characteristics.
A digital signal processing circuit or the like in the mobile telephone set is constituted by a silicon LSI chip, and is sealed with resin. If the surface of a surface vibrating element such as a surface acoustic wave filter is covered with sealing resin, however, the vibration of the surface vibrating element is restrained, degrading the characteristics thereof. Consequently, it is impossible to seal the movable element with resin.
Therefore, an internal circuit in the mobile telephone set is constructed by mounting a surface acoustic wave filter element on a wiring substrate in addition to an LSI package such as the digital signal processing circuit. Therefore, the miniaturization of the wiring substrate has a limitation, which prevents the mobile telephone set from being miniaturized.
An object of the present invention is to provide a semiconductor device capable of containing a movable element, together with a semiconductor chip having other functional elements formed thereon, in the same package.
In order to attain the above-mentioned object, the present invention is directed to a semiconductor device, characterized by comprising a semiconductor chip having a connecting pad formed on its surface, a surface movable element overlapped with and joined to the surface of the semiconductor chip and having a movable element and a connecting pad formed on its surface opposite to the semiconductor chip, and a pad joint for connecting the connecting pad on the surface of the semiconductor chip and the connecting pad on the surface of the surface movable element to each other and ensuring an operating space for allowing an operation of moving the movable element between the semiconductor chip and the surface movable element.
According to this construction, the connecting pads are connected to each other by the pad joint in a state where the surface, where the movable element is formed, of the surface movable element is opposite to the surface of the semiconductor chip, and the semiconductor chip and the surface movable element are overlapped with and joined to each other, so that a semiconductor device having a so-called chip-on-chip structure is constructed. The operating space for the movable element is ensured between the opposite surfaces of the semiconductor chip and the surface movable element by the function of the pad joint. Consequently, the semiconductor chip and the surface movable element can be sealed with resin, for example, and contained in the same package without degrading the characteristics of the movable element. Consequently, the movable element, together with the semiconductor chip having other functional elements formed thereon, can be contained in the same package, thereby making it possible to miniaturize an electronic equipment using the movable element.
It is preferable that the pad joint is a metal raised portion provided on the connecting pad of the semiconductor chip or the surface movable element. The metal raised portion in this case may be a so-called bump obtained by raising a metal by plating, or may be a metal evaporated film which is not raised so high as the bump.
According to this construction, the semiconductor chip and the surface movable element are overlapped with and joined to each other by the metal raised portion provided on the surface of the semiconductor chip or the surface movable element, thereby making it possible to ensure the operating space between the surfaces of the semiconductor chip and the surface movable element.
The movable element may be a surface acoustic wave element, which includes a surface acoustic wave filter element.
According to this construction, the operating space is ensured between the opposite surfaces of the semiconductor chip and the surface movable element. Accordingly, the characteristics of the surface acoustic wave element using the surface acoustic waves propagating through a surface layer of the surface movable element are satisfactorily held.
It is preferable that the semiconductor device further comprises a peripheral edge joint arranged between the semiconductor chip and the surface movable element for joining the semiconductor chip and the surface movable element to each other and surrounding a peripheral edge of the surface movable element.
According to this construction, the semiconductor chip and the surface movable element -are joined to each other by the peripheral edge joint surrounding the movable element, so that the operating space for the movable element can be blocked from an external space. When the semiconductor chip and the surface movable element are sealed with resin, for example, and contained in the same package, therefore, the characteristics of the movable element can be reliably prevented from being changed by the sealing with resin, for example.
It is preferable that the peripheral edge joint is provided at the peripheral edge of the surface movable element, that is, outside an area where the movable element is formed.
The peripheral edge joint may be composed of the same material as that of the pad joint. In this case, the pad joint and the peripheral edge joint can be formed at the same step.
Furthermore, the peripheral edge joint may be constituted by a metal raised portion provided on the surface of either one of the semiconductor chip and the surface movable element. When the pad joint and the peripheral edge joint are composed of the same material, it is preferable that the peripheral edge joint is also provided on either of the semiconductor chip or the surface movable element 1 on which the pad joint is provided.
The pad joint and/or the peripheral edge joint may be constituted by metal raised portions provided on both the semiconductor chip and the surface movable element. In this case, the metal raised portions respectively provided on the semiconductor chip and the surface movable element are joined to each other.
It is preferable that the peripheral edge joint is composed of a conductive material.
In this case, if the conductive peripheral edge joint is connected to a low impedance portion (for example, a power supply portion or a ground portion) of the semiconductor chip or the surface movable element, the peripheral edge portion can function as an electromagnetic shield. Consequently, it is possible to reduce the effect of external noises on elements arranged in a space inside the peripheral edge joint.
It is preferable that a shielding film composed of a metal is formed on a reverse surface that is a surface opposite to the surface, where the movable element is formed, of the surface movable element.
According to this construction, the movable element can be shielded magnetically and electrically by the shielding film. If the shielding film is connected to the low impedance portion such as the power supply portion or the ground portion, the shielding film can function as an electromagnetic shield, thereby making it possible to further stabilize the characteristics of the movable element.
In a case where the peripheral edge joint is composed of a conductive material, if the peripheral edge joint and the shielding film are electrically connected to each other, the shielding effect can be further increased.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.